my explanation is better considering I was hung over....

 

Can someone from Pfadt respond to the no benefit allegations presented here?

 

I think the Pfadt rear mount is self explanatory.

The stock mount s of a corvette are like a triangle, two mount in the front and one in the rear on the differential.

Th Pfadt rear mount changes the triangle to a four way mount by extending the mounting locations, which reduces the ability of the transmission to rock either left or right.

Add a DTE brace and you limit the vertical (rotational) aspect.

If you got high powered street or track car this combo should tighten up your drive train flex.

I will be installing one of the Pfadt rear mounts when I do some work over the winter, as I already have the DTE brace.

 

You are right that the torque that is developed in the transmission and differential will be reacted back trough the torque tube to the engine mounts.

However, the problem with the transmission and differential shaking is still persistent. This is because the torque tube is not an infinitely stiff member. Just like the sway bar in your car the torque tube twists with the applied torque. Now you have an undamped spring (torque tube), mass (transmission/differential) system that is fixed at the engine side and free to rotate and the transmission side. This free oscillation of the transmission and differential is the "wheel hop" that many feel.

The Pfadt C5 Transmission mount removes the free end of the spring/mass system to eliminate this oscillation.

I hope that this helps. If you have any questions please let me know!

 

Josh, still wondering about all the remaining undamped springs in the system.
Will the brace help with wheel hop, or will it eliminate wheel hop?

 

Josh,

Please help me understand ... I've been lurking on this thread and two things keep bothering me ...

1) The GM mounting is rubber, so I agree that there is some flex built into it. I guess I buy into the idea that the torque tube could flex under high torque loads. What I don't get is how your mount, which has polyurethane pads "attaching" it to the crossmember, not a welded or bolted attachment, eliminates flex any more than the GM part does. In fact I could argue that the GM part has some, but not infinite, flex in it. Your polyurethane pads theoretically have "infinite" flex built in as they can slide across the crossmember an unlimited distance.

2) I was taught that a 3 point mount is always preferable to a 4 point mount. The analogy used is a bar stool. Get two bar stools ... one with 3 legs, and one with 4. Place each stool on a very uneven floor and the 3 legged stool (3 point mount) is naturally stable ... all 3 legs ALWAYS continue to touch the floor. A four legged stool on an uneven floor becomes unstable ... one leg is always off the floor and sometimes two opposed legs could be off the floor ..... it is a "naturally" unstable stool (mount). Flex in the drivetrain creates that "uneven floor". As torque "distorts" the drivetrain it seems to me a 3 point mount is a much better solution.

Help me understand where I've gone "off the rails" here .....

 

With the Pfadt Transmission Mount you are fixing both ends of the spring and no longer allowing it to oscillate.

As for the help or cure see Chips experience here!

 

Wheel hop is caused by a number of issues. No one product is going to fix all the causes of wheel hop.

Wheel hop is caused by;

Uneven roads (bumby roads) that cause the skip feeling.

To stiff sidewall tires (runcraps), low profile ties with little or no side wall flex.

Poor suspension set-up (to stiff).

 

Sorry I missed you. You posted while I was writing.

To address #1.
The Polyurethane pads can not move and infinite distance. The are constrained to move in an arc defined by the distance from the center bolt. So initially they move completely vertical, this vertical movement is resisted by one of the two pads against the sub-frame. Thus constraining the system from excessive rotational movement.

To address #2
You are absolutely right that this mount will over constrain the system. If your goal was to produce a car with minimal manufacturing tolerances then yes, you would want only three points to mount this system. However, the flaw in this system is it allows too much movement and thus degrades performance. We provide you with shims to place under each pad to minimize any manufacturing tolerances in the sub frame. Since you are also mounting the system in a compliant material you reduce the effect of this over constrained system. Just as if you set a four legged stool on a soft rubber mat all the legs will touch the ground.

Please let me know if there are any other questions! I am happy to help!

 

Chip didn't get wheel hop in an hour of testing, but he also has poly control arm bushings. I can sometimes go for an hour too. Depends on tire and road temperatures, road surface, tire inflation pressure, etc.
I figured you had more experience with it than Chip does. That's why I was asking you.

 

In our testing the Pfadt C5 Transmission mount has eliminated the powertrain shake that is sometimes mistaken as wheel hop.

 

OK, but what about actual wheel hop (which is what mine is)?

 

You are looking in the wrong direction to cure actual wheel hop. There are a number of problems that can be associated with wheel hop: Chassis stiffness, spring rate, shock damping, sway bars, bushing compliance, tire compound, tire stiffness, sprung mass, unsprung mass, etc... The problem is the natural frequency of the rear end is close to the input frequency from the tire slip/grip cycle. You need to change the natural frequency of the system. This is done quickly by changing to a set of Pfadt Coil Overs. The increase in spring rate and change in shock damping drastically change the natural frequency and usually eliminate the experienced wheel hop.

There are too many factors that go into this complex problem to say that any one change is going to eliminate the problem. The solution I provided is the most substantial change that you can easily do, and is the reason I suggest it.

Please let me know if there is anything else that I can help with. Good Luck!

 

Josh,

Can you please quantify a few of your comments? What exactly do you mean by “excessive rotational movement” and “the flaw in this system is it allows too much movement and thus degrades performance.” What is too much movement and how did your company measure it?

Thanks,

Eric D

 

Eric,

Under car video. Like this one that shows the movement in the motor mounts on a C6 Z06. Notice that even with the engine mounts installed you can still see the rear end moving in the factory transmission mounts.

See the video Here

One could argue that you want no rotational movement of the drivetrain relative to the chassis. That, of course, is not practical in a street car. When designing the C5 transmission mount we took a cue from the C6 transmission mounts. The C6 uses a pair of transmission mounts that are located either side of the transmission, similar to your engine mounts. The Pfadt C5 Transmission mount allows some of the torque from the transmission/differential to be carried through the sub-frame rather then through the torque tube to the engine mounts.

 

Josh,

Are videos the only measurement technique, if not what else is used? Do you have a video of your new differential mount showing its function compared to the stock mount?

Unless I'm mistaken, the C6 mounts look like they are designed to take care reacting torque from the wheels as their primary job. Does your new differential mount control the wheel reacting torque in the differential?

Eric D

 

Getting me confused.

I thought this thread was about the C5 rear mount and not the C6 mounts.

I'm not really to interested in the C6's as I don't really care for their body lines.

If something is anchored more towards the center like the C5's stock transmission mount and you moved the mounts more outward, it would follow that this would provide better stabilization.

Very similar to cars track width, a wider track width provides better stability and thus a higher "G" force, all things being equal.

Why do most solid axle rear drive cars have the axle mounted on each side ? Because it balances out the axle when torque is applied. Same principal except on an independent rear.

It looks like you own a stock corvette so maybe this product wouldn't do much for you, but I believe guys with bigger horsepower and torque would definetly benefit from the rear tranny mount.

 

The principle is very different on an independent rear with a torque tube.

Eric's asking good, valid questions. I don't know if his car is stock, but mine isn't, and I'm interested in the answers. I imagine others are too.

 

Yeah, how so ???




Is Eric going to buy one ??

To me, Eric seems to be asking the same question in different ways and goating the OP. If he has something to add to the discussion great, if not stop badgering Josh.

 

Read the thread. It's already been summarized.



Is he going to buy one?
If the value of adding a torque reaction member, in a car that's designed not to have a torque reaction on that axis, is explained to the satisfaction of an automotive engineer, who knows what he might do?
Anyway, the forum isn't just for people who are considering a product purchase.

In a couple of different current threads, the Pfadt guys are handling questions with dignity and a great attitude.
I think they'll be OK.